This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-048327, filed Feb. 25, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an integrated circuit device fabricated by integrating many electronic circuits such as amplifier circuits, and a liquid crystal display apparatus and, more particularly, to an integrated circuit device designed to reduce bias current deviations between chips, and a liquid crystal display apparatus using the integrated circuit device as an amplifier circuit for a driver circuit.
A display driver circuit in a conventional liquid crystal display apparatus comprises first memory elements which are equal in number to pixels required for one horizontal line and used to store a digital video signal (to be referred to as an RGB signal hereinafter), a shift register for transferring a timing pulse for storing the RGB signal, second memory elements for further storing the RGB signal stored in the first memory elements in a cycle of one horizontal period, a group of D/A converters (DACS) for converting the RGB signal stored in the second memory elements into an analog value, and a group of amplifier circuits for receiving the RGB signal converted by the group of DACs into the analog value and driving signal lines and liquid crystal cells of the liquid crystal display panel. Each liquid crystal cell to which the voltage of the RGB signal converted into the analog value is applied changes in transparency in accordance with the voltage value, thereby determining the brightness of the corresponding pixel.
In this case, a bias current for the group of amplifier circuits is set in accordance with a bias signal generated by one bias circuit. More specifically, a current Ibias generated in the bias circuit is supplied to a diode-connected transistor in the bias circuit, and the gate voltage of this transistor is applied to each amplifier circuit of the group of amplifier circuits.
In each amplifier circuit, the gate voltage of the diode-connected transistor is applied to a gate of a transistor and converted into a current. This converted current is used as a bias current in each amplifier circuit. That is, the transistors of the bias circuit and amplifier circuit constitute a current mirror circuit. The transistors of the bias circuit and amplifier circuit respectively serve as the input- and output-side transistors of the current mirror circuit.
Although the number of amplifier circuits included in the group of amplifier circuits depends on the specifications of a liquid crystal display apparatus, an apparatus using amorphous silicon TFTs for a liquid crystal display panel uses as many as 3,000 amplifier circuits. It is therefore difficult to integrate the group of amplifier circuits into one chip. For this reason, such amplifier circuits are generally fabricated into a plurality of chips. In this case, a bias circuit is provided for each chip. In general, one chip incorporates about 300 amplifier circuits.
These amplifier circuits are integrated to be arrayed in a chip. The input-side transistor (the transistor of a bias circuit) of a current mirror circuit is placed on either end of this amplifier circuit array. For example, the input-side transistor is placed beside the amplifier circuit on the left end.
MOS transistors are generally used as the transistors of a bias circuit and amplifier circuit. In general, MOS transistors deviate in threshold voltage (Vt) within a certain range between different chips and within the same chip. Assume that the transistors of amplifier circuits deviate in threshold voltage. Even in this case, if the number of amplifier circuits in one chip is as many as 300, the transistors of the amplifier circuits generally exhibit little difference, even between different chips, in the manner in which the threshold voltage deviates.
If, however, the diode-connected transistors in the bias circuits deviate in threshold voltage between chips, bias currents flowing in the transistors in the amplifier circuits deviate in accordance with the deviations in threshold voltage, resulting in differences in current consumption and characteristics between the chips. The difference in current consumption between the chips greatly affects the power supply design of the liquid crystal display apparatus, and hence is undesired. In addition, the deviations in characteristics between the chips lead to a deterioration in the image quality of the liquid crystal display apparatus.
As described above, according to the bias circuit arrangement for the amplifier circuits used for the conventional liquid crystal display apparatus, bias currents flowing in many transistors of the amplifier circuits in chips deviate between the chips, resulting in differences in current consumption and characteristics between the chips.
It is an object of the present invention to provide an integrated circuit device which reduces deviations in bias current between chips to reduce differences in current consumption and characteristics between the chips and a liquid crystal display apparatus which realizes easy design by using the integrated circuit device as a driver circuit and reduces a deterioration in image quality.
According to the present invention, there is provided an integrated circuit device comprising a plurality of electronic circuits, and a current mirror circuit constituted by a plurality of diode-connected input-side transistors which receive an input current for setting a bias current and are distributed to the plurality of electronic circuits, and a plurality of output-side transistors which respectively supply output currents corresponding to the input current, as bias currents, to the plurality of electronic circuits, wherein the plurality of electronic circuits and the current mirror circuit are integrated into one chip.
According to the present invention, the plurality of electronic circuits are arrayed and integrated within the chip, and the input-side transistors are distributed to and arranged in every L (L is an integer not less than one) electronic circuits of the plurality of electronic circuits.
According to the present invention, the plurality of electronic circuits are arrayed and integrated within the chip, and only P (P is an integer satisfying Pxe2x89xa6M) diode-connected input-side transistors in every M diode-connected input-side diodes are connected to each other so as to constitute current mirror circuits.
As described above, according to the integrated circuit device of the present invention, the plurality of diode-connected input-side transistors are arranged, which constitute the current mirror circuit, together with the output-side transistors for generating bias currents in the respective electronic circuits, and these input-side transistors are distributed and arranged, thereby making the averages of deviations in the threshold voltages of the input-side transistors of the respective chips become almost equal to each other between the chips. This therefore improves the matching between the input-side transistors and output-side transistors, and reduces differences in current consumption and characteristics between the chips.
According to the present invention, there is provided a liquid crystal display apparatus comprising a liquid crystal display constituted by a plurality of pixels, signal lines for selectively supplying video signals to the respective pixels and scanning lines crossing the signal lines, a driver circuit including a group of amplifier circuits which amplify video signals and supply the signals to the signal lines and drives the signal lines, and a selector circuit which selects the scanning lines, wherein the group of amplifier circuits are integrated into a plurality of chips in units of a predetermined number of amplifier circuits, each of the chips including integrated current mirror circuits fabricated by a plurality of diode-connected input-side transistors which receive an input current for setting a bias current, and a plurality of output-side transistors which respectively supply output currents corresponding to the input current, as bias currents, to the amplifier circuits, and the plurality of input-side transistors are distributed to and arranged in the plurality of amplifier circuits incorporated in the respective chips.
As described above, if a group of amplifier circuits in a driver circuit for a liquid crystal display apparatus is fabricated by using the integrated circuit device of the present invention, a liquid crystal display apparatus can be realized, which allows easy design of a power supply, in particular, because of small differences in current consumption and characteristics between the chips, and exhibits little deterioration in image quality due to deviations in characteristics.
According to the present invention, there is provided an integrated circuit device comprising a plurality of output transistors which receive a setting voltage for setting a bias current and supply output currents as bias currents to electronic circuits, a plurality of monitoring transistors which are distributed to and arranged in the plurality of electronic circuits and output monitoring currents upon reception of the setting voltage, and an amplifier which amplifies a voltage corresponding to a difference between the monitoring current and a set input current and outputting the setting voltage.
According to the present invention, there is provided a liquid crystal display apparatus comprising a liquid crystal display constituted by a plurality of pixels, signal lines for selectively supplying video signals to the respective pixels and scanning lines crossing the signal lines, a group of amplifier circuits which amplify video signals and supplying the signals to the signal lines, a driver circuit which drives the signal lines, and a selector circuit which selects the scanning lines, wherein the group of amplifier circuits are integrated into a plurality of chips in units of a predetermined number of amplifier circuits, and each of the chips comprises a plurality of output transistors which receive a setting voltage for setting a bias current and supplying output currents as bias currents to the amplifier circuits, a plurality of monitoring transistors which are distributed to and arranged in the plurality of amplifier circuits and output monitoring currents upon reception of the setting voltage, and an amplifier which amplifies a voltage corresponding to a difference between the monitoring current and a set input current and outputting the setting voltage.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.